Known falling film heat exchangers generally have a number of vertically oriented tubes located in a housing. A first flowable medium for heat exchanging is arranged to fall under gravity through the tubes, while a second flowable medium is fed into the housing. Due to temperature differential between the first medium and the second medium, heat is transferred from one medium to the other medium through the tube walls. Such known heat exchangers are typically used in an evaporator and/or a condenser in processes for obtaining potable water from sea water or brackish water.
The inventor has noted that the first flowable medium contacts a relatively small portion of the inner wall surface of each tube while flowing therethrough. Accordingly, only a small portion of the available heat transfer surface area of each tube is in direct heat transfer with the first medium. The known heat exchangers are therefore relatively inefficient.
The first flowable medium generally contains impurities and/or minerals that cause fouling or scaling by depositing some of the impurities and/or minerals on the inner wall surfaces of the tubes. Fouling/scaling reduces the heat exchange transfer rate across the tube walls. The level of fouling/scaling increases progressively with the amount of the flowable medium through the tubes. In time, the deposited impurities and/or minerals would increase to a level that the heat exchangers become ineffective. Thus, the impurities and/or minerals on the inner wall surfaces of the tubes must be removed. Removal of the impurities and/or minerals require removal of the heat exchangers from service so that the tubes can be cleaned mechanically and/or chemically. Considerable costs and time are required to maintain a process plant employing the known heat exchangers in a reasonably effective working order. In addition, during maintenance, the plant is not productive.